Method for manufacturing polarization-independent orbital angular momentum modulator

An orbital angular momentum beam generator, comprising:

• a light source;
• a polarization controller having an input connected with the light source;
• a polarization-independent orbital angular momentum modulator connected with an output of the polarization controller;
• and
• a first optical fiber jumper connected with an end of the polarization-independent orbital angular momentum modulator, the end of the polarization-independent orbital angular momentum modulator being away from the polarization controller;
• wherein the polarization-independent orbital angular momentum modulator comprises:
• an optical fiber body having a spiral optical fiber structure having a long-period optical fiber grating effect;
• and
• the optical fiber body has a periodic spiral refractive index modulation in an axial direction;
• and the spiral refractive index modulation is distributed in an axial direction, a radial direction, and an angular direction of the optical fiber body and configured to excite the spiral phase to generate an orbital angular momentum beam;
• the optical fiber body being formed by:
• heating, in a heating area, the optical fiber body to a molten state;
• twisting the optical fiber body evenly and at a speed while in the molten state, thereby generating a stress in the optical fiber body;
• and
• removing the twisted optical fiber body from the heating area;
• and
• freezing the removed twisted optical fiber body such that the stress generated during twisting is frozen into the optical fiber body.